1. Field of the Invention
The present invention relates to an image heating apparatus and a heat generating rotary member for use therein such as an image fixing device for use in an image forming apparatus of the electrostatic recording type, such as a copying machine, a facsimile machine, and a printer. More particularly, the invention relates to an image heating apparatus and a heat generating rotary member for use therein such as an image fixing device for fixing toner images, which uses the electromagnetic induction heating system.
2. Description of the Related Art
Recently, market demands for the energy saving and high operation speed are increasing in the image forming apparatus such as a copying machine, a facsimile machine, and a printer. To meet the demands, it is important to improve the thermal efficiency of the image fixing device used in the image forming apparatus.
In the image forming apparatus, an unfixed toner image is formed on a recording medium such as a recording sheet, a printing sheet, a photo sensitive sheet, or an electrostatic recording sheet, by an image transfer system or a direct system, and by an image forming process such as electrophotography recording process, electrostatic recording process or a magnetic recording process. An image fixing device based on such a contact heating system as a heat roller system, a film heating system, or an electromagnetic induction heating system is widely used for the image fixing device for fixing the unfixed toner image.
As for the image fixing device of the electromagnetic induction heating type, Japanese Unexamined Patent Publication No. H08-022206 discloses a technique which generates Joule heat is generated by an eddy current generated in a magnetic metal member by an alternating magnetic field applied thereto, and heats a heating bar including the metal member in an electromagnetic induction manner.
However, in this technique, it is a common practice to exclusively use a magnetic metal, such as ferritic stainless, iron, or Permalloy, for a heating part of the image fixing device. A nonmagnetic metal, such as aluminum, copper or titanium, has not been used for the heating part of the image fixing device. In this respect, there is still a need for improvement of the heating efficiency of the heating part.
To solve the problem stated above, the present invention presents the following solutions.
According to an aspect of the invention, there is provided a fixing roller for use in an image fixing device, wherein the fixing roller includes a magnetic metal layer and a non-magnetic metal layer, and the nonmagnetic metal layer is provided on the outer side of the magnetic metal layer, and is thinner than the magnetic metal layer.
Preferably, the fixing roller is a heating roller.
Furthermore, the fixing roller is a heating roller, and the non-magnetic metal layer contains copper.
Still further, the fixing roller is a heating roller, and the non-magnetic metal layer contains copper, and a thickness of the non-magnetic metal layer is within a range from 5 to 20 xcexcm.
Furthermore, the image fixing the thickness of the magnetic metal layer is larger than 20 micrometers but equal to or smaller than 50 micrometers.
In the image fixing device using the thus constructed fixing roller, heat is more efficiently generated than in the image fixing device using a fixing roller formed with a single magnetic metal layer.